Three alleles of the vitamin D receptor (VDR) gene have been identified and homozygosity for one allele (BB or Bb, respectively) have been associated with reduced bone mass. The present protocol proposes to test the hypothesis that the BB or Bb VDR gene alleles are predictive of postmenopausal osteoporosis. VDR gene alleles and bone mass will be determined in 100 women with established osteoporosis and 100 women with normal bone mass and segregation of the alleles with bone mass will be determined.